Neurofibromatosis (Recklinghausen's disease) is a congenital and familial disease presenting abnormalities of the skin, nervous system, bones, and soft tissues. A classic case demonstrates (1) multiple soft, elevated cutaneous tumors (fibroma molluscum), (2) cutaneous pigmentation (café au lait spots), and (3) neurofibromas of peripheral nerves, frequently palpable in the subcutaneous tissue. In addition to this “cardinal triad” of diagnostic findings may be seen elephantoid soft-tissue masses on the body and fan-like enlargements of peripheral nerves called “plexiform neuromas.” Incomplete varieties of the disease (formes frustes), showing only cutaneous pigmentation, also occur; these cases frequently progress to the complete picture later in life. In the last few decades, the variety of skeletal defects associated with neurofibromatosis has received increasing attention. These are of particular interestto the radiologist, since certain types are characteristic of the disease, while others are most suggestive. Associated abnormalities include severe scoliosis, defects of the walls of the orbits, erosive defects caused by adjacent neurogenic tumors, bowing and pseudarthrosis of the lower leg, and disorders of growth of bone associated with elephantoid hypertrophy of soft tissue. Knowledge of these findings enables the radiologist to help confirm the clinical diagnosis. On occasion, he may be able to predict the diagnosis from the skeletal changes before it has been established clinically. That neurofibromatosis is a disease involving neurectodermal (60) tissues has long been accepted as fact. The term “neurectoderm” refers to that portion of the primitive ectoderm which forms the neural groove and gives rise to the nervous system. Mesodermal elements also have shown abnormalities. In earlier years, the consensus was that these mesodermal abnormalities were always secondary to and a result of the abnormal neurectodermal elements; more recently, it is being recognized that mesodermal dysplasia is a basic component of the disease, not depending on neurectodermal dysplasia for its explanation. The present study will help to confirm this view. Background Historical: Recklinghausen (48), in 1882, introduced the term “neurofibromatosis” and presented the first adequate description of the histologic changes. He contended that the tumors were chiefly fibrous, arising from mature connective tissue of the nerve sheaths, especially the endoneurium. Descriptions of the clinical manifestations of neurofibromatosis had been published previously. Recklinghausen credited Tilesius (64) with the first adequate description of fibroma molluscum in 1793. Smith (57), in 1849, published a remarkable volume reporting in great detail two cases of generalized neurofibromatosis, with necropsy and pathologic observations.